[Eeglablist] Ground electrode location

Jeff Eriksen eriksenj at ohsu.edu
Wed Jun 26 12:35:56 PDT 2013


Darren,

The head placement of the ground electrode should only affect the
common-mode rejection of environmental electrical noise (mainly 60 Hz).
Typically one would want to place the ground on the midline, somewhat
frontally, especially if you have subjects looking at a monitor that might
be emanating 60 Hz. This will optimize the 60 Hz rejection. On the other
hand, if you do not have a problem with 60 Hz, or have a good way to
filter it out (not using a notch filter!), the ground placement is not
critical. To be clear, the placement of the ground will not affect
symmetry in any way (except for the symmetry of the 60 Hz noise).

The reference is the location all the other electrodes are measured
against, and should be on the midline as well, if you want the waveforms
to look symmetric across the midline. Cz is a natural position, but the
midline posterior to Cz will work as well. If you are going to
re-reference anyway, the placement of the Ref electrode is not critical
either.

-Jeff Eriksen


On 6/26/13 6:49 AM, "Darren Tanner" <dstanner at gmail.com> wrote:

>Hi all,
>
>Can anyone let me know if it's problematic to place the ground electrode
>over one hemisphere (rather than, say, the midline)? Due to convenience
>reasons, we may be ordering some caps which have the ground electrode
>over a right hemisphere site. My understanding is that the location of
>the ground electrode on a conventional EEG system should not matter (in
>contrast to the location of the reference electrode, which does matter),
>but I wanted to be sure that putting it on the right hemisphere would not
>introduce any hemisphere asymmetries in the effects.
>
>Thanks!
>Darren
>
>-----------------------------------------
>Darren Tanner, Ph.D.
>Postdoctoral Scholar
>Bilingualism and Language Development Lab
>Center for Language Science
>Department of Psychology
>Penn State University
>
>
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